The present disclosure relates generally to renewable power generation systems and, more particularly, to a system and method for integrating wind pumped and hydroelectric energy storage systems.
Wind is one of the fastest growing renewable energy resources. Turbines, which use the kinetic energy of wind to generate mechanical energy, convert the mechanical energy to electricity. Wind turbines typically have two or three blades that are faced into or away from the wind. As the wind causes the blades to rotate, the shaft in the turbine spins. The mechanical energy generated may be used to power certain tasks, such as pumping water for example, or the mechanical energy may be converted to electricity. When connected to a generator, the spinning of the shaft drives a generator, which in turn produces electricity.
However, the intermittent nature and variable speed of wind are the major drawbacks of wind generation systems, thus resulting in low system availability and low penetration. Existing solutions to the intermittency problem of wind power generation devices (such as through the use of energy storage systems) have traditionally either been cost prohibitive or have low energy efficiency. Another way to mitigate intermittency and increase system availability is to use wind generation in parallel with other generating sources, which can be complimentary to the wind. It has been observed that in certain locations of the world, wind and hydro show complimentary patterns of availability, both on a daily basis and a seasonal basis.
Pumped hydroelectric storage is one of the more economically viable energy storage methods. At times of low electrical demand, excess electrical capacity is used to pump water into an upper reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine, thereby generating hydroelectricity. Reversible turbine/generator assemblies can act as both pump and turbine. Some facilities, for example, use abandoned mines as the lower reservoir, while others use the height difference between two natural bodies of water or artificial reservoirs. As a result of evaporation losses from the exposed water surface and mechanical efficiency losses during conversion, about 60% to about 85% of the electrical energy used to pump the water into the elevated reservoir may be regained from this process. This compares relatively favorably with respect to other energy storage devices such as some types of batteries and hydrogen fuel cells.
Notwithstanding the respective advantages of wind generated power systems and hydroelectric storage systems, the challenges of integrating wind with pumped hydroelectric storage (as well as with loads in both grid-connected and stand-alone systems) while, at the same time, optimizing energy usage and maintaining transient stability have not been adequately addressed. In addition, problems such as frequency and voltage references, pump and generation mode transition, interaction with power electronic interfaced loads, and stand-alone operation still need to be solved.
Moreover, there are no directly integrated, wind-pumped hydro systems presently in operation. Most of the documented or proposed systems are intended to function at high power levels and are operated only as grid-connected systems. Accordingly, it would be desirable to implement an integrated, wind-pumped hydroelectric system that provides a cost effective solution to the intermittency issue, for both grid-connected and stand-alone applications.